Import scene into VSE with different camera size
You need to add a Transform Effect strip and adjust the settings to fit, however, this can be a tedious process, so here is a script that will simplify the process:


First, run or install this script:
https://raw.githubusercontent.com/tin2tin/blender-reset-aspect-ratio/master/reset-aspect-ratio.py
Add a transform strip to your strip that needs rescaling. 
Select the Transform strip.
In the Sidebar find the Reset Aspect Ratio and click it.